The goal of this project is to test the in vivo efficacy of anti-HIV immunotoxins (ITs). Degylcosylated ricin A-chain (dRAC) has been coupled to monoclonal anti-HIV antibodies to construct ITs that kill HIV-infected cells. The activity of antibodies directed toward gp4l is enhanced 30 to 100-fold by soluble CD4, so that in the presence of CD4 these ITs show approximately 10,000-fold selectivity in culture systems A chimeric IT containing CD4 attached to the toxic portion of pseudomonas exotoxin A (CD4-PE40) shows similar activity in vitro but failed clinical trials. The hypothesis to be tested in the proposed studies is that experimental ITs aimed at gp4l are less toxic and have better pharmacokinetic properties than CD4-PE40. This hypothesis will be tested in a model using irradiated NOD/LtSz-scid mice, which have defects in NK cells and complement activity, as well as the scid mutation. The animals are implanted with human lymphoma cells persistantly infected with molecularly cloned HIV NL3-4. In culture, greater than 99 percent of these cells are infected with HIV; when injected into irradiated NOD/LtSz-scid mice, the cells establish tumors in various sites and persistantly shed detectable p24 antigen into blood and show high numbers of infectious viruses in spleen cells from the animals. The specific aims are to test the efficacy of anti-HIV ITs using this mouse model and to study the pharmacokinetics of candidate ITs in the same model.